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G. L. HUNTER and A. W. LISHMAN

Summary.

By means of ovarian examination and teasing with vasectomized rams, the intervals to first post-partum ovulation and oestrus were determined in a 23-factorial experiment with twenty-four German Merino ewes which lambed between 28th October and 15th November 1966. First ovulation occurred 32·1 ± 1·9 (8 to 45) days after lambing. Three, fifteen and six ewes had none, one or more than three silent ovulations respectively, before showing heat after a mean interval from lambing for all ewes of 57·1±4·5 days. The regression of post-partum interval to ovulation (Y) on ewe's weight 3 days post partum (X) was significant (P<0·01) ; for ewes weighing 83 to 162 lb, Y = 55·15–0·21X. The regression of post-partum interval to oestrus on ewe's weight was not significant, and neither were the effects of treatments, namely, weaning at 3 or 20 days post partum, supplementary feeding of 0 or 1 lb maize grain daily from 3 to 28 days post partum, and joining with vasectomized rams at 3 or 14 days post partum.

J. S. Crichton, A. W. Lishman, M. Hundley and C. Amies

Summary. Wethers (at least 2½ years after castration) were implanted with testosterone propionate (TP), oestradiol dipropionate (ODP), dihydrotestosterone, or a combination of dihydrotestosterone and ODP Silastic capsules. Active immunization against both oestradiol and oestrone or oestradiol only was used to negate effects of oestrogens produced by aromatization of TP. On exposure to oestrous ewes, immunization of wethers implanted with TP significantly (P < 0·01) reduced all components of mating behaviour (except sniffing and Flehmen) to levels seen in untreated controls. The results support the conclusion that dihydrotestosterone potentiates the action of oestrogens, particularly as regards Flehmen, and has no action on its own within the central nervous system, while oestrogens do not restore mating activity to the same level as that following treatment with testosterone.

B. P. LOUW, A. W. LISHMAN, W. A. BOTHA and J. P. BAUMGARTNER

Prolactin is readily secreted before and during oestrus in ewes (Kann, 1971; Cumming, Brown, Goding, Bryant & Greenwood, 1972) and Denamur, Martinet & Short (1973) indicated that this hormone has a luteotrophic effect. Although these findings suggest that prolactin contributes to normal reproduction in ewes, the physiological rôle of the prolactin surge at oestrus has as yet not been elucidated.

In the rat and mouse, a surge of prolactin on the afternoon of pro-oestrus promotes luteolysis of corpora lutea (Malven & Sawyer, 1966; Grandison & Meites, 1972). Such an effect appears unlikely in sheep since luteal regression in this species commences several days before the onset of oestrus (Deane, Hay, Moor, Rowson & Short, 1966).

Prolactin is also rapidly released into the circulation in response to the milking stimulus in lactating ewes (Fell, Beck, Brown, Catt, Cumming & Goding, 1972) and it has been suggested that the secretion of large

Five experiments were conducted with the objective of developing a method to induce superovulation in ewes with a single i.m. injection of FSH. This was achieved by injection of 10 mg FSH-P in propylene glycol at the same time as luteolysis was induced by cloprostenol on day 13 of the oestrous cycle (day 0 = oestrus). Experiments 1, 2, 3 and 5 were conducted in a single flock of Manchega ewes in Spain during the breeding season. Ovulation rates were determined at laparoscopy. In Expt 1, FSH-P was diluted in saline, and neither 5 mg FSH on day 1 nor 5 or 10 mg FSH-P on day 13 changed the ovulation rate after cloprostenol treatment on day 13. In Expt 2, FSH-P was diluted in propylene glycol and data were collected over 2 years. Ten milligrams FSH-P, on day 13 only, increased (P < 0.01) the mean number of corpora lutea to 5.5 compared with a control value of 1.5. Five milligrams FSH-P on day 13 only had no effect; however, 5 mg FSH-P on day 1 reduced the mean number of corpora lutea formed in ewes receiving 10 mg FSH-P on day 13 to 2.6 (P < 0.01). Saline and propylene glycol, as vehicles for 10 mg FSH-P, were compared directly at two times of injection in Expt 3. FSH-P increased the mean number of corpora lutea when injected on day 13 in propylene glycol (4.7) but not in saline (2.5; P < 0.5). Ovulation rate did not differ between diluents when FSH-P was injected 24 h before cloprostenol (1.3; day 12). Experiments 4 and 5 were conducted to examine possible mechanisms by which propylene glycol improved the response to FSH. In Expt 4, conducted during anoestrus in a crossbred flock in West Virginia, concentrations of FSH in plasma were measured for 58 h after injection of 10 mg FSH-P in saline or propylene glycol. Propylene glycol did not delay the time of maximum concentration of FSH in plasma after i.m. injection (2.7 ± 0.7 h) when compared with saline injection (3.6 ± 0.5 h). Maximum concentration was reached later when FSH-P was injected s.c. in propylene glycol (7.6 ± 0.7 h; P < 0.05). In Expt 5, ovulation rate was greater (P < 0.05) in ewes treated with 10 mg FSH-P in propylene glycol than in ewes treated with FSH-P in saline and an injection of propylene glycol at a separate site. The number of corpora lutea did not differ in ewes treated with FSH-P in saline and in ewes treated with FSH-P in saline and propylene glycol at a separate site. Thus neither delayed absorption nor an augmentation effect could account for the benefit of propylene glycol as a vehicle for delivery of FSH to superovulate ewes.

Departments of Animal Science and Biochemistry, University of Natal, Pietermaritzburg, South Africa

The anoestrous condition which follows upon periods of underfeeding in ewes is apparently similar to the normal seasonal anoestrus and is usually manifested as a prolongation (Hunter, 1962) or precipitated onset (Smith, 1962) of the seasonal period of sexual rest. It has been suggested that the ovarian quiescence noted in underfed animals may be the result of pseudohypophysectomy (Mulinos & Pomerantz, 1940; Lamming, 1966; Leathem, 1966).

An acute release of LH at oestrus in ewes has been demonstrated by Niswender, Roche, Foster & Midgley, 1968; Goding, Catt, Brown, Kaltenbach,Cumming & Mole, 1969; Wheatley & Radford, 1969) and it is possible that changes in the pattern of LH release may indicate functional changes in the pituitary of ewes which become anoestrous after periods of inanition. This phenomenon was studied in an attempt to elucidate the mechanism involved in a